1. Field
The following description relates to an envelope tracking (ET) current bias circuit and a power amplifier applied to a power amplification system to efficiently remove a direct current (DC) offset current from an ET current, based on an envelope of an input signal.
2. Description of Related Art
In general, average power tracking (APT) or envelope tracking (ET) are used as a method to reduce electric current consumption of a power amplifier module (PAM).
The APT technique is a method to increase efficiency by adjusting an electric source voltage (VCC) according to average output power. The ET technique is a method to increase efficiency by controlling the electric source voltage of a power amplifier (PA) according to an envelope of a radio frequency (RF) signal.
The ET technique is a method to reduce the average consumption of electric current by decreasing the electric source voltage of PA from a portion of the RF signals that have a relatively low level of amplitude, and to prevent the linearity thereof from being degraded by increasing the electric source voltage of PA in a portion of the RF signals that have a relatively high level of amplitude.
In addition, the APT technique is a method to provide VCC calculating an average value of an envelope signal for a predetermined period of time. Also, because the ET technique provides VCC calculating an instantaneous value of an envelope signal, ET modulators are separately required.
A power amplifier may include an ET bias circuit to reduce the consumption of electric current. ET bias circuits may include an envelope detection circuit and a voltage/current converting circuit to detect an envelope signal of an input signal.
However, because the envelope detection circuit provides an ET voltage, based on the envelope of the input signal, and the ET voltage includes an undesirable DC offset voltage, such DC offset voltage and the ET voltage are converted into an electric current in the voltage/current converting circuit. Therefore, there is a limitation in which an unnecessary DC offset current is included in the ET current output from the voltage/current converting circuit.